In a study of the effects of a combination of carbon monoxide and nicotine on tissue and functional changes in rats it was found that subconvulsive doses of nicotine (0.5 to 1.0 mg nicotine bitartrate/kg) plus exposure to moderate to severe levels of carbon monoxide (100 to 500 ppm) produced within 4 hours hypothermia, elevated blood glucose and lactic acid levels, with the lowest concentrations of the noxious agents, and elevated plasma aspartate and alanine aminotransferases levels at the highest concentrations. The study thus far has shown that the effects of a combination of nicotine and carbon monoxide induced greater systemic changes than either agent alone. This finding emphasizes the importance of possible synergism between various individual components of cigarette smoke and the effects that such interactions have upon physiological, biochemical and pathological changes in animals and man.